Systems and methods for removing undesired metal within vias from printed circuit boards

Abstract

A method is provided for modifying a via from a PCB including a plurality of subassemblies comprising a plurality of layers. The method may include drilling a via of the PCB to form a through-hole to remove an unwanted material in the via of the PCB. The method may also include depositing a carbon-based material over an inner wall of the through-hole. The method may further include back drilling a first portion of the through-hole by a drill from the top of the PCB to form a first blind via. The method may also include selectively plating a conductive material over the carbon-based material to form a plated through-hole.

1 . A drill for use in back drilling of a PCB, the drill comprising:
 an inner core comprising a conductive material;   a continuous outer coating layer disposed over the inner core, the outer coating layer comprising a first cutting portion, a second cutting portion opposite to the first cutting portion, the first and second cutting portions comprising a conductive material and extending from a bottom of the inner core; and   a non-conductive coating disposed over a portion of the outer coating layer between the first and second cutting portions.   
     
     
         2 . The drill of  claim 1 , wherein the portion of the outer coating layer between the first cutting portion and the second cutting portion is under the bottom of the inner core. 
     
     
         3 . The drill of  claim 1 , wherein the non-conductive coating comprises diamonds. 
     
     
         4 . The drill of  claim 1 , wherein each of the first and second cutting portions comprises a tip pointing downward from the bottom of the inner core. 
     
     
         5 . The drill of  claim 1 , wherein the inner core has a substantially cylindrical shape. 
     
     
         6 . The drill of  claim 1 , wherein the conductive material of the inner core comprises one of carbide, tungsten, or cobalt. 
     
     
         7 . The drill of  claim 1 , wherein the first and second cutting portions have a depth from 0.010 inches to 0.020 inches. 
     
     
         8 . The drill of  claim 1 , wherein the first cutting portion has a shape substantially symmetric to the second cutting portion from a vertical centerline of the inner core. 
     
     
         9 . The drill of  claim 1 , wherein each of the first and second cutting portions have an angle θ less than 75° from an outer edge. 
     
     
         10 . The drill of  claim 1 , wherein the drill is configured to back drilling a first portion of a through-hole from a top of a PCB to form a first blind via, 
     
     
         11 . The drill of  claim 10 , wherein the drill stops drilling at an internal conductive trace of the PCB when the drill touches the internal conductive trace of the PCB, wherein the internal conductive trace is grounded during back drilling such that the drill accurately stops at the internal conductive trace that is grounded during back drilling. 
     
     
         12 . The drill of  claim 10 , wherein the drill has a diameter larger than the through-hole of the PCB. 
     
     
         13 . The drill of  claim 10 , wherein the drill is configured to back drilling a second portion of the PCB below the through-hole from a bottom of the PCB to form a second blind via. 
     
     
         14 . (canceled) 
     
     
         15 . A method of modifying a via of a PCB to form a stub-less through-hole, the method comprising:
 drilling a via of the PCB comprising an unwanted material to form the stub-less through-hole by removing the unwanted material in the via of the PCB;   depositing a seed material directly over an inner wall of the through-hole, wherein the seed material is a seed for plating a conductive material;   back drilling a first portion of the through-hole by using a drill comprising a drill bit from a top of the PCB to form a first blind via, wherein the drill drills through the seed material,   grounding an internal conductive trace of the PCB during the back drilling such that when the drill touches the internal conductive trace of the PCB, the drill automatically stops drilling at the internal conductive trace of the PCB, wherein the internal conductive trace is in contact with a sidewall of the through-hole; and   selectively plating the conductive material over the seed material to form a stub-less plated through-hole.   
     
     
         16 . The method of  claim 15 , wherein the first blind via is larger than the through-hole having a first diameter. 
     
     
         17 . The method of  claim 15 , wherein the conductive material does not adhere to the first blind via. 
     
     
         18 . The method of  claim 15 , wherein the first blind via is aligned with the through-hole. 
     
     
         19 . The method of  claim 15 , further comprising back drilling a second portion of the PCB below the through-hole from a bottom of the PCB to form a second blind via. 
     
     
         20 . The method of  claim 15 , wherein the conductive material comprises copper.